1. Field of the Invention
The present invention concerns the field of piston rings for a sliding piston within a cylinder employed in an internal combustion engine, compressor or a piston pump.
It is known in the art that in general the particular objective of one of the rings is to collect the lubricant deposited on the cylinder wall and to send it back to the crankcase. This ring is generally known as the "scraper ring".
The invention is more particularly concerned with a scraper ring including a washer, as well as a scraping skirt which includes a truncated portion open towards the crankcase and presenting, at one end, a scraping line which comes in contact with the cylinder wall. The washer is used for mounting the ring in a "support" groove of the piston.
2. Description of Related Art
This type of scraper ring is in particular described in French Pat. Nos. 81.02353, 81.24100 and 82.00625 as well as corresponding U.S. Pat. No. 4,516,481. These patents describe several ways of producing a scraper ring composed of a flat washer on the outer edge of which is joined a truncated scraping skirt whose extended line is free and extends to a scraping line contact with the cylinder wall.
The applicants have carried out numerous tests on this type of ring. During this operational testing, several technical problems were encountered in certain situations when, during operation, the washer was subject to radial frictional forces in this groove. Radial freedom of movement of the washer in its groove is important for trouble-free functioning of the scraper ring when, during operation, the piston is subject to slight radial movements within the limit of its clearance within the cylinder. These movements should be accommodated by sliding motion of the washer in the piston groove so that the ring does not lose uniform pressure of contact with the cylinder along part of its circumference leaving corresponding zones on the cylinder which are not properly scraped.
By continuing their research, applicants discovered that a substantial axial distance between the scraping line and the median washer plane of the ring had the effect of producing a rocking moment on the washer causing it to bind in the scraper ring groove, with resilient radial friction, interfering with desired radially free functioning of the scraper ring. This technical problem involves all scraper rings which include a substantially flat washer as support for the scraper ring and a scraping line which is located axially, substantially outside of the median plane of the washer. It has been the subject of studies and experiments on the part of the applicants to their discoveries and developments of the scraper ring of the present invention.